Abstract Lymphatic metastasis is the predominant route of the initial spread of breast cancer cells and their presence in regional lymph nodes is the single most clinically important negative prognostic factor. Once in lymph nodes, breast cancer cells can find their way into the circulation and spread to distant sites. This being the case it is critically important for us to develop models that will allow us to define mechanisms fo the initial invasion of tumor cells into lymph vessels and to develop platforms for screening drugs that target those mechanisms. Our working hypothesis is that 3D models that recapitulate the interactions between breast carcinoma cells and lymphatic microvascular endothelial cells can be used to identify druggable pathways associated with invasion into lymphatic vessels and lymphangiogenesis. Our rationale is that the pathways identified in vitro will recapitulate at leas a subset of those present in patient samples and thereby allow us to define druggable nodes for novel therapeutic strategies. Critical to translation of our studies will be screening platforms tht can be used to reproducibly grow breast and lymphatic cells in 3D and test and quantify dynamic responses of live cells to therapeutic interventions in real-time. Our Specific Aims are to: 1) Establish optimal conditions for recapitulating in vivo interactions between breast carcinoma cells and lymphatic microvascular endothelial cells; 2) Design, fabricate and test novel microfluidic platforms that can be used for imaging, identification of therapeutic targets and drug screening; 3) For proof-of-principle studies, Identify a candidate therapeutic target and validate in patient samples; and 4) Perform initial screening of agents that target the candidate therapeutic target. We will use innovative 4D (3D + time) cultures to model the interactions between human breast carcinoma cells and human lymphatic microvascular endothelial cells. We will construct novel microfluidic platforms for long-term growth of the novel 3D cultures, image the cultures by confocal microscopy, analyze biochemical and immunochemical pathways that are altered by the dynamic interactions in these cultures, identify potential therapeutic targets and screen drugs directed against those targets and associated pathways. Effective screening requires that our models be highly reproducible and that we use platforms that allow us to test many different drugs at multiple concentrations. We have extensive experience in constructing miniaturized platforms that can be used for cell culture, including as prosthetic devices in patients. Our studies should accelerate the identification of effective drugs potentially ones targeted to individual patients.